This invention relates to an extruded, monovinyl aromatic polymer foam comprising a monovinyl aromatic polymer with a broad molecular weight distribution of certain configuration. This invention further relates to a process for making the foam.
Historically, chlorofluorocarbons were employed as blowing agents in making monovinyl aromatic polymer foams for insulating applications. The foams provided excellent insulation performance of long duration.
Due to concerns over potential ozone depletion, hydrochlorofluorocarbons such as 1-chloro-1,1-difluoroethane (HCFC-142b) have largely replaced chlorofluorocarbons as a blowing agent in insulating monovinyl aromatic polymer foams. Such foams provide excellent insulating performance while exhibiting substantially lower ozone depletion potential.
It may be desirable to employ blowing agents which exhibit further reduced or zero ozone depletion potential. Possible agents include carbon dioxide and 1,1,1,2-tetrafluoroethane (HFC-134a).
A problem with employing blowing agents such as carbon dioxide or HFC-134a is they exhibit relatively high vapor pressures and low solubility in melts of monovinyl aromatic polymers. As a result, extrusion foaming systems employing them can experience processing problems such as high pressure drop and high die pressure and product problems such as poor skin quality, high density, and small foam cross-section.
It would be desirable to develop an extrusion process wherein processing problems could be reduced and desirable product properties maintained. It would be further desirable to develop a polymer resin substrate which facilitated the attainment of same.